Quantitative Evaluation of Deformation Induced Martensite in Austenitic Stainless Steel Using Magnetic NDE Techniques

The goal of the present study is to examine the applicability of non-destructive magnetic hysteresis loop technique and Hall effect sensor to characterize the strain induced alpha '-martensite in an austenitic stainless steel. For this purpose, eight different levels of tensile deformation, from 0.05 to 0.44 true stain values, were applied and corresponding induced martensite fractions were determined, using X-ray diffraction method. Finally, magnetic hysteresis loop and Hall effect methods were applied. Results show that major outputs of hysteresis loop (maximum flux density, retentivity and coercivity) and Hall effect (real part, imaginary part, modulus and phase angle for the 3rd harmonic) are significantly affected by variations in the induced martensite fraction. Besides, a new parameter, amplitude and shape of raw received signal, was used in this study. The established relationships with high correlation coefficients between electromagnetic outputs and martensite fraction indicate the potential of the proposed methods to be used for detecting the microstructural changes in AISI 304 stainless steel subjected to different strains.